1. Field of the Invention
The present invention relates to an etching method for use in connection with semiconductor device fabrication and to a method of fabricating a semiconductor device using the same, and more particularly, to a method of etching a carbon-containing layer using a new etching gas and to a method of fabricating a semiconductor device using the same.
2. Description of the Related Art
As semiconductor devices have become more integrated and the feature size thereof has correspondingly decreased, the horizontal areas of the semiconductor devices have also decreased while the thicknesses of such semiconductor devices have increased. As a result, the heights of unit elements and contacts for electrically connecting the unit elements have increased, and thus, the aspect ratios of the corresponding contact holes have also increased. In the etching process for forming a pattern having such an increased aspect ratio, the thickness of a layer to be etched is greater and there is essentially no etching process margin due to the height of the photoresist pattern that needs to be used. Therefore, the thickness of the photoresist layer is decreased, and a relatively thin photoresist layer leads to a number of problems. To solve the problems associated with the photoresist pattern being thin, a technique of using an amorphous carbon layer (ACL) as an etch mask has been developed (See U.S. Patent Laid-open Publication No. 2004/0079726 A1), the disclosure of which is incorporated herein by reference.
An etch mask including an ACL for forming a fine pattern of a highly-integrated semiconductor device (on the scale of microns or smaller) may be an etch mask including a multilayer structure in which an ACL, a capping layer, and a photoresist layer are sequentially stacked on a film to be etched on a substrate. In this case, a photoresist pattern is formed through exposure and development processes, and that pattern is transferred to an anti-reflection layer and the capping layer, thus producing a capping layer pattern. The ACL is etched using the capping layer pattern as a first etch mask, and the capping layer pattern is thereby transferred to the ACL, thus producing an ACL pattern. The thus formed ACL pattern is then used as a second etch mask for etching the film to be etched on the substrate. After the film to be etched is etched, residues and etching byproducts of the ACL pattern are removed through ashing and stripping processes.
The ACL of the etch mask having the multilayer structure as described above includes carbon as a primary component. Accordingly, an etching gas commonly including O2, N2, or a combination thereof may be used to etch the ACL. The capping layer interposed between the ACL and the photoresist layer is preferably formed of a material, for example, SiON or SiO2, which has strong etch resistance to components (such as O2 and N2) which are used as the ACL etching gas, and which also enables low-temperature deposition.
However, as semiconductor devices have become more highly integrated and the width of unit elements has correspondingly decreased, the thickness of the photoresist layer has become reduced, and, accordingly, the thickness of the capping layer has also become reduced. When etching an ACL using a relatively thin capping layer as a first etch mask, the etch selectivity between the capping layer and the ACL layer becomes a critical factor in obtaining an excellent sidewall profile of an ACL pattern to be used as the second etch mask in the succession of etching steps. Particularly, when an ACL is etched using plasma, the capping layer is sputtered by ions, thereby additionally degrading the etch resistance of the capping layer.
In the prior art, to increase the etch resistance of a relatively thin capping layer used as an etch mask for etching an ACL, a fluorocarbon series gas may be injected so that a protective carbon series polymer is stacked on the capping layer. However, since an ACL includes carbon as a primary component, an etching gas that includes N2 or O2 must be used to etch the carbon. Thus, when etching the ACL using an etching gas that also includes the fluorocarbon series gas, it is difficult to deposit the protective carbon series polymer on the capping layer, and, accordingly, a desired etch selectivity of the ACL relative to the capping layer is difficult to obtain.
To form a fine pattern, e.g., a contact hole pattern, that is beyond the ordinary resolution limit of a photolithographic process, the shape of a hole (as defined by an etch mask) that is needed to form the contact hole or other fine pattern is commonly required to have a smaller critical dimension (CD) in the bottom or lower portion thereof than in the top or upper portion, which is an inlet of the contact hole. Accordingly, the ACL pattern obtained by etching the ACL should preferably be formed with an inclined or cone-shaped sidewall profile to reduce the CD of the bottom of the hole relative to the inlet opening at the upper portion of the hole. To obtain such an inclined sidewall profile, a polymer acting as an etch mask could be deposited on sidewalls of the hole being formed by etching the ACL. However, it is difficult to etch the pattern with the inclined sidewall profile following such polymer deposition.
These and other problems with or limitations of the prior art techniques are overcome in whole, or at least in part, by the methods of this invention.